1. Field of the Invention
The present invention relates generally to columns used as structural support in buildings. More particularly, it concerns a filament wound composite architectural column having thin tubular walls with axial load bearing capacity.
2. The Background Art
Until now, fiber-reinforced composite structures involving low-grade bonding agents have not generally been used as load-bearing structural supports. Although fiber-reinforced composites are known to provide excellent resistance to tensile and bending loads, structural compression-loaded supports, such as architectural columns, have been generally confined to reinforced concrete, steel, and large timbers.
There has been a clear pattern in the art to confine application of fiber-reinforced composite materials to articles subject to either tensile or bending loads. For example, composite materials have been used to make ropes (U.S. Pat. No. 4,257,309, issued on Mar. 24, 1981 to Dunahoo), bending spring supports (U.S. Pat. No. 5,368,358, issued on Nov. 29, 1994 to Christensen) tubular members for use as golf shafts, hang gliders spars and the like (U.S. Pat. No. 5,261,980, issued on Nov. 16, 1993 to Pearce), and even utility poles for supporting electric power transmission lines (U.S. Pat. No. 4,769,967, issued on Sep. 13, 1988 to Bourrieres). However, these and other composite articles are subject mainly to flexural and tensile stress and not to significant axial compressive stress.
Although applications involving fiber-reinforced composite materials continue to expand, composites appear to remain confined in their use to resisting bending and tensile loads but not direct axial loads, or as a combination with steel or concrete. The thinking in the field of structural compression members has been that the higher-density materials are necessary to provide the compressive strength needed in structural columns. For example, although U.S. Pat. No. 5,218,810 (issued on Jun. 15, 1993 to Isley, Jr.) teaches the use of composites to produce a structural column, the composite material is limited in use as a fabric reinforcement layer surrounding a reinforced concrete column. Further, the Isley patent teaches application of the composite reinforcement "to increase the column's resistance to structural failure when subjected to asymmetric loading" (col. 2, lines 16-18), suggesting that the composite reinforcement is contemplated to provide resistance to flexure stress and not to direct axial loading.
It is known to manufacture structural columns in accordance with traditional architectural column design. Ionic and Doric orders of architectural column design have been employed to provide a tapered design to vertical columns. Tapered ornamental column supports have evolved in some aspects of their design but not in terms of the core materials used for their manufacture. For example, U.S. Pat. No. 5,327,694 (issued on Jul. 12, 1994 to Gamel et al.) discloses a tapered ornamental column comprising a tubular member made from cardboard and urethane foam, but the tubular member surrounds a reinforced concrete core member which bears the applied loads. Architectural columns have generally comprised solid, nontubular core members made from concrete or steel.
In view of the clear trend to favor use of composites for applications as members or to members in tension or bending, it is doubtful that others have sought to make structural columns from composite materials, especially those involving low-grade polyester systems. Those having ordinary skill in the field of columns are even less likely to contemplate a thin wall, tubular composite architectural column design, especially in view of the centuries-old tendency to build structural columns from concrete or steel.